The Backstage backend comes packaged with a basic HTTP proxy, that can aid in reaching backend service APIs from frontend plugin code. See Call Existing API for a description of when the proxy can be the best choice for communicating with an API.
The plugin is already added to a default Backstage project.
const proxyEnv = useHotMemoize(module, () => createEnv('proxy')); const service = createServiceBuilder(module) .loadConfig(configReader) /** ... other routers ... */ .addRouter('/proxy', await proxy(proxyEnv));
Configuration for the proxy plugin lives under a
proxy root key of your
# in app-config.yaml proxy: '/simple-example': http://simple.example.com:8080 '/larger-example/v1': target: http://larger.example.com:8080/svc.v1 headers: Authorization: $env: EXAMPLE_AUTH_HEADER
Each key under the proxy configuration entry is a route to match, below the
prefix that the proxy plugin is mounted on. It must start with a slash. For
example, if the backend mounts the proxy plugin as
/proxy, the above
configuration will lead to the proxy acting on backend requests to
The value inside each route is either a simple URL string, or an object on the format accepted by http-proxy-middleware.
If the value is a string, it is assumed to correspond to:
target: <the string> changeOrigin: true pathRewrite: '^<url prefix><the string>/': '/'
When the target is an object, it is given verbatim to
except with the following caveats for convenience:
changeOriginis not specified, it is set to
true. This is the most commonly useful value.
pathRewriteis not specified, it is set to a single rewrite that removes the entire prefix and route. In the above example, a rewrite of
'^/api/proxy/larger-example/v1/': '/'is added. That means that a request to
/api/proxy/larger-example/v1/some/pathwill be translated to a request to
There are also additional settings:
allowedMethods: Limit the forwarded HTTP methods. For example
allowedMethods: ['GET']enforces read-only access.
allowedHeaders: A list of headers that should be forwarded to and received from the target.
By default, the proxy will only forward safe HTTP request headers to the target.
Those are based on the headers that are considered safe for CORS and includes
last-modified, as well as all headers that are
set by the proxy. If the proxy should forward other headers like
authorization, this must be enabled by the
allowedHeaders config, for
allowedHeaders: ['Authorization']. This should help to not
accidentally forward confidential headers (
The same logic applies to headers that are sent from the target back to the frontend.